ABC News' Carolyn Durand and Katie Kindelan report:

Duchess of Cambridge Kate Middleton's last solo royal engagement before she gives birth to her first child next month involved the smashing of a champagne bottle, but there was no scandal here for the beloved duchess.

The duchess, 31, fulfilled a royal tradition today by becoming another in the long line of royal women to christen a cruise ship, in her case, Princess Cruises' newest ship, the 3,600-passenger Royal Princess.

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Duchess Kate, appearing without husband Prince William, wore a leopard-print coat by Hobbs, a popular chain retailer in the U.K., that highlighted her growing baby bump. She also maintained the high fashion she has sported throughout her pregnancy by wearing black high heels and a black fascinator.

The duchess, due to give birth in July, told the gathered guests, "I name this ship Royal Princess, may God bless her and all who sail in her," before cutting the rope.

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The traditional Champagne bottle was then released and sent into the ship's hull, smashing to a large cheer from the crowd and a slight wince from the duchess.

Duchess Kate is part of a long cruise ship tradition of choosing godmothers "to bring good fortune to the ship and its passengers while at sea," Karen Candy, spokeswoman for Princess Cruises, told ABCNews.com in April when it was announced she would be the ship's godmother.

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Princess Diana, Kate's late mother-in-law, christened a cruise ship at the same spot in Southampton in 1984.

"It's like a rite of passage for the beautiful women of the royal family," ABC News' royal consultant Victoria Murphy said.

Duchess Kate has maintained a busy public profile during her pregnancy after a bout of extreme morning sickness left her hospitalized in the early weeks of her pregnancy. Now, say royal experts, the duchess is expected to lie low and nest, just as any expectant first-time mother would do.

"She's not going to be running around with a bump that size so I think she'll be putting her feet up, relaxing, spending time with her family and spending time with William," Murphy said. "[She'll be] playing the waiting game."