Always in the lead, Without Parole owned by Triple Crown winner Justify's part owner John Gunther beat U S Navy Flag cross the wire with ease. The second favourite Tip Two Win placed fourth behind Wootton.
US Navy Flag's stablemate Gustav Klimt ran on well from off the pace to finish second.
Gosden said: "US Navy Flag had gone, and Frankie said, 'I had to go after him. I was frightened he had got three lengths, and in the end I went a bit soon'.
Owner/breeder John Gunther said in an interview to TimeForm magazine: "It is a dream come true. In all the 20 years I have been coming to Royal Ascot, my dream was just to have a horse run at Royal Ascot. Then we start in a Group One and do it; I don't know what to say.
"This does mean more [than breeding Triple Crown winner Justify] and always will. This was the most important and means everything to me. To be able to mate the mare to Frankel and Juddmonte giving me that nomination even though the mare was unproven. To go through all that and then watch Without Parole being raised as a yearling was so special.
"The mare had not proven herself but, after we bred her to Frankel, she got her G1 winner [Tamarkuz] and proved herself. Juddmonte allowing me to bred that mare to Frankel meant everything, believe me, because I love Frankel so much.
"John Gosden and Frankie. What a team! They are unbelievable."
Click Here To Watch St James Palace Stakes winner Race 2018
1st Without Parole (J. Gosden,F. Dettori), 2nd Gustav Klimt (A. O'Brien,D. O'Brien), 3rd Wootton (H. Pantall,M. Barzalona), 4th Tip Two Win (R. Teal,D. Probert), 5th Kings Shield (J. Gosden,O. Murphy), 6th Gabr (S. Stoute,J. Crowley), 7th Romanised (K. Condon,S. Foley), 8th Threeandfourpence (A.O'Brien,S. Heffernan), 9th U S Navy Flag (A. O'Brien,R. Moore), 10th Chilean (M. Meade,S. Sousa)
Distance:7f 213yd (1,603 metres), Surface:Turf, Track:Right-handed, Qualification:Three-year-old colts, Weight:9 st 0 lb, Purse:£400,000 (2017),1st: £226,840
Credit: Pallavi Shevade pallavi.shevade@secretaristworld.com