Michael Phelps, Wife Nicole Announce Pregnancy on Instagram

United States Olympic gold medalist Michael Phelps and his wife, Nicole, are expecting their second child. 

Phelps posted the couple's pregnancy announcement in an Instagram post Tuesday:

The couple's first child, Boomer Robert Phelps, was born in May 2016. The pair got engaged in 2015 and were married in a secret ceremony in June 2016. 

Phelps is the most decorated Olympic athlete in history. The 32-year-old won 28 Olympic medals in swimming from 2004 to 2016, including 23 gold medals. 

After the 2016 Olympics in Rio de Janeiro, at which he won six medals, Phelps officially retired from competition.