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Pete Wentz and his model girlfriend Meagan Camper are expecting their first baby together. 

The Fall Out Boy bassist shared the news on Instagram Monday, initially using emoticons to explain that "man plus woman equals baby."  Wentz added in a more conventional language that he and Camper are "super excited" about the announcement, and posted a photo of the happy couple cuddling. 

Wentz and Camper have been together for three years.  He was previously married to pop singer Ashlee Simpson, with whom he already has a five-year-old son.  Wentz and Simpson divorced in 2011, and Simpson recently announced her engagement to pop icon Diana Ross' son Evan Ross.